Hi- I'm very curious to hear more about your stubborn tomatoes and overwintering them! I'm in Sydney, Australia which has a fairly similar climate to Southern California so I'd like to attempt overwintering if it's possible. What do you do to keep the plants healthy over a long period of time? Do you trim back branches, give any particular treatments..? Any info at all would be very welcome.
Thanks heaps,
Slashy

Here is a link that might be useful: My MyFolia garden profile

I used to see cherry toms growing feral year-round in south florida - tomato is a tropical plant after all. I wonder though, if most of the "heirlooms" aren't adapted to higher latitudes? So they may be sensitive to daylentgh for blooming and fruit-set. I'm no tom expert - you'll get the answers right quick over at the tomato forum.

There is a plant hormone called "Blossom Set" which helps with just your type of situation. Most larger garden centers sell it -- it's in a spray can, you just spray in on the blossoms. The above poster is probably correct -- your problem is most likely due to climate or daylength factors. You might try applying a trace element supplement around your plant, too -- sometimes, peppers, eggplants, and tomatoes won't set if they're deficient in certain micronutrients (I think it's selenium, but can't remember). I know garden centers sell a trace element supplement fertilizer, but can't remember the name. Or, you could sprinkle about half a cup of any complete vitamin tablet around the base of the plant and water in well, this would do the same thing.

If your plant isn't in a windy area, the blossoms might not be pollinating. Tomatoes are self-pollinating, and the wind shakes the plant enough to get the pollen to move to the right spot. If the plants have access to bees, they will land on the flowers and "sonicate" - vibrate - to pollinate the blossoms efficiently.

If you don't have wind or bees, give the plants a gentle shake. Some have used electric toothbrushes to replicate the bees sonicating - there are threads about this on the Tomato forum. Such threads also dismiss the "blossom set" products, but if the problem isn't access to wind or bees maybe that would help.